1. Field of the Invention
The present invention relates to a construction of a radiation image taking apparatus that uses a radiation detection means. In particular, the present invention relates to a technique suited for the designation of an image taking direction of an object with respect to a radiation image taking apparatus.
2. Related Background Art
Conventionally, a film/screen method, with which radiation image taking is performed by combining a photosensitive film (X-ray detection means) serving as a two-dimensional detection plane with a phosphor having sensitivity to X rays, has been most commonly used to take an X-ray image. In addition, in recent years, a method called “computed radiography (CR) method” has also been put into practical use. This method is a system where a radiation transmission image is first accumulated as a latent image in an imaging plate serving as a two-dimensional detection plane and then the latent image is read out from the imaging plate by irradiating excitation light onto the imaging plate. Aside from this, with the recent advancement of a semiconductor process technique, an apparatus has also been developed which takes an X-ray image in a like manner using an X-ray detection sensor composed of multiple photoelectric conversion elements as a two-dimensional detection plane. A system of this type has an advantage that it is possible to record an image having an extremely wide radiation exposure range as compared with the conventional radiograph system using a photosensitive film. That is, after X rays in a wide dynamic range are read with the X-ray detection sensor and are converted into an electrical signal, a radiation image is outputted as a visible image to a recording material (such as a photosensitive material) or a display apparatus (such as a CRT) using the electrical signal, thereby making it possible to obtain a radiation image that is hard to be influenced by variations in radiation exposure amount.
FIG. 22 is a schematic diagram showing a radiation image taking system that uses the semiconductor sensor described above. In an X-ray image taking apparatus 2201, an X-ray detection sensor 2202 is embedded which has a detection plane where multiple photoelectric conversion elements are arranged in a two-dimensional manner. With this construction, X rays emitted from an X-ray generation portion 2203 are irradiated onto an object 2206 and X rays transmitted through the object 2206 are detected by the X-ray detection sensor 2202. An image signal outputted from the X-ray detection sensor 2202 is subjected to digital image processing in an image processing means 2204 and is displayed on a monitor 2205 as an X-ray image of the object 2206. Such an X-ray detection sensor is called “planar detector”, “flat panel”, or the like due to its shape.
When image taking is performed with the various systems described above, in order to position the object in a detection area of the detection means, it is required to indicate the detection area of the detection means and the like on the enclosure of the planar detector. A method for displaying the detection area of the detection means on the enclosure of the planar detector is proposed in Japanese Patent Application Laid-Open No. 2002-291730.
FIG. 23 shows an example of a conventional transportable planar detector. In this drawing, reference numeral 2301 denotes a transportable X-ray image taking apparatus in which an X-ray detection sensor (not shown) is embedded which has a detection plane where multiple photoelectric conversion elements are arranged in a two-dimensional manner. Reference numeral 2302 indicates a cover for an enclosure plane of the X-ray image taking apparatus 2301 in a portion where X rays are irradiated, with the cover being made of a material having a high X-ray transmittance and being a carbon plate or the like. Reference numeral 2303 represents a rectangular frame line representing the detection plane of the X-ray detection sensor (not shown). Reference numeral 2304 denotes a center line in a short-side direction of the rectangular detection plane and reference numeral 2305 indicates a center line in a long-side direction thereof. Reference numeral 2307 represents a cable connecting the X-ray image taking apparatus 2301 to a control apparatus (not shown), with electrical signals that are control signals and an electronic image being communicated between the X-ray image taking apparatus 2301 and the control apparatus through the cable. Reference numeral 2308 denotes an object, with a case where the object 2308 is a right hand of a person being illustrated in the drawing as an example. In FIG. 23, the upper left corner of the frame line 2303 is set as the image coordinate original point of the X-ray detector (not shown). Also, in the drawing, the downward direction is set as the positive direction of an X axis and the rightward direction is set as the positive direction of a Y axis.
FIG. 24 is an explanatory diagram of a case where an image taken with the X-ray image taking apparatus 2301 is displayed on a monitor 2401. In this drawing, reference numeral 2403 denotes an object and reference numeral 2402 indicates an image area. In this illustrated case, a definition has been formulated in advance so that an image coordinate original point is positioned at the lower left corner of the display apparatus.
FIG. 25 shows a case where the same X-ray image taking apparatus 2301 as in FIG. 23 is set under a state where it has been rotated by 180°. The same reference numerals as in FIG. 23 denote the same members. In this drawing, the image original point is changed to the lower right corner, although the cover 2302, the frame line 2303, and the center line 2304 have symmetric shapes and therefore are not changed from their states shown in FIG. 23. Consequently, if image taking is performed by determining the detection plane for the object 2308 in the same direction as in FIG. 23 without giving consideration to the fact that the X-ray image taking apparatus 2301 has been rotated by 180°, image displaying on the monitor 2401 is performed in the manner shown in FIG. 26 where an object 2601 is displayed under a state where it has been rotated by 180° from the state of the object 2403 shown in FIG. 24. That is, in this case, the object is not displayed in an original observation direction.
As described above, when image taking is performed using a transportable X-ray image taking apparatus or an X-ray image taking apparatus embedded in a bed, various relative positional relationships between the two-dimensional detection plane and the object are possible, which leads to a problem in that it is not guaranteed that a taken image is displayed in a desired direction at the time of image displaying. Also, there is a case where printing is performed by inserting an object name, an image taking date and time, and the like (hereinafter referred to as the “annotation”) in the upper portion or the like of an electronic image. In this case, there occurs a problem in that the positional relationship between the annotation and the object does not become a desired relationship at the time of displaying.
In the conventional example described above, even in the case shown in FIG. 26 where the image is displayed in a direction that is different from the original direction, it is possible to obtain the same positional relationship as in FIG. 24 by rotating the image, although this results in a situation where the convenience of the system, whose advantage lies in the immediacy of image displaying is lost. It is possible for an operator to define in advance the correspondence between the coordinate original point and the coordinate system of a taken image and a display portion of the display apparatus at the time of displaying, although it is usual that this correspondence is defined in units of parts to be image-taken. Therefore, when the same part is image-taken in different directions like in this example, there occurs a problem in that it is impossible to perform displaying in a desired direction without delay.